Just How Many Tyrant Lizard Kings Populated Earth?

By Jim Brace-Thompson

As America begins evaluating its latest census data, a census of a different sort has been tallied recently; namely, a census of how many creatures would have had us as appetizers had we co-existed!

I’m talking about Tyrannosaurus rex, or the “tyrant lizard king” of the Cretaceous Period. Researcher Charles R. Marshall (University of California, Berkeley) always wondered just how many T. rex individuals there were in all and how dense their populations may have been at any one time. Fortunately for him, T. rex is one of the most extensively studied of all dinosaurs. Thus, he and his team of fellow researchers had a good amount of data from which to work. Still, their methods involved a lot of extrapolation based on body mass and population distribution and densities of existing creatures, as well as good old-fashioned guess work. (I’ll spare you the detailed mathematical formulas and the margin-of-error.)

In a cover story for the April 16, 2021, issue of the journal Science, Marshall and his colleagues suggest at least 2.5 billion T. rex trod Earth during their reign 68 to 66 million years ago. At any one time, there may have been 20,000 individuals thundering across North America. These individuals left a genetic legacy that persisted across some 127,000 generations until an unexpected asteroid from space took the last ones out.